1. Field of the Invention
The present invention relates to a full range bar code scanner, more particularly, to a bar code scanner having a wider reading range without the distance restriction in scanning the bar code signals.
2. Description of the Prior Art
A conventional bar code scanner, as shown in FIGS. 1 and 2, contains a scanner housing 1 inside of which a light source 2, a lens set 3 and a CCD-sensing device 4 are disposed. The light source 2 shines on a bar code 5 in front thereof, and the reflection light 6 is focused by the lens set 3 and the image of the bar code 5 is formed on the CCD-sensing device 4. After read by the CCD-sensing device 4 and decoded by an electrical circuit, the image is converted into digital data for use.
As described above, the scanning distance at which a clear image is formable is not the same because of the difference of the curvature of the lens set 3 and the focus design between the lens set 3 and the CCD-sensing device 4. The principle thereof is similar to that of the diopter of the spectacles and the magnifying glass. Being too far will cause a difficult recognition due to the insufficient brightness and the small image. Being too near will cause a difficult forming of image or the image-forming range beyond the capacity of the CCD-sensing device 4. Therefore, the effective distance (depth of focus, symbolized by "X") of the reflection light of the bar code upon the CCD-sensing device 4 is fixed. Accordingly, the reading distance of the conventional bar code scanner is restricted by the lens set 3 in such a way that the image of the bar code beyond the standard reading range can't be formed on the CCD-sensing device 4. As a result, the conventional scanner designated for reading a remote bar code is not suitable for reading a bar code within a short distance. In the contrary, the scanner for reading a bar code within a short distance isn't suited for reading a remote bar code. In addition, the depth of focus "X" of the common scanners for recognizing the bar code is not enough, causing the inconvenience in using that the user has to repeatedly adjust the distance between the scanner and the bar code.